Phonons, Rotons, and Layer Modes of Liquid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>H</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow><mml:mi>e</mml:mi></mml:math>in Aerogel

Fåk, B.; Plantevin, O.; Glyde, H. R.; Mulders, N.

doi:10.1103/physrevlett.85.3886

Cited by 29 publications

(109 citation statements)

References 29 publications

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“…Under confinement the excitation spectrum develops two distinct branches: a bulk-like phonon-roton spectrum associated with liquid in the center of the pore and a new branch due to a compressed layer of liquid at the pore surface. This behavior has been observed in a wide variety of confining media and has been shown, in Vycor, to explain the observed behavior of the heat capacity and superfluid fraction [10][11][12][13] . The effects of confinement on the roton remain an open question in contrast to the bulk where the behavior is quite well understood.…”

Section: Introductionsupporting

confidence: 52%

Bulklike excitations in nanoconfined liquid helium

et al. 2017

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The effects of confinement, disorder, and reduced dimensionality upon quantum fluids have been studied by the adsorption of liquid helium in porous media. The effects of extreme, nanoscale confinement upon its microscopic excitations are not presently understood. Several previous experiments have suggested that, at sufficiently low temperature, the roton mean free path is set by the restricted geometry. Here we show that the lifetime of the roton excitation is unaffected when superfluid helium is confined within cylindrical pores only a few nanometers in diameter. The temperature-dependence of its lifetime are found to be identical to the bulk fluid, implying that the lifetime is not set by the scale of the confinement. Our results demonstrate that the rotons in the pore center propagate without being modified by the confining media, unlike the collective excitations of classical fluids.

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Section: Introductionsupporting

confidence: 52%

Bulklike excitations in nanoconfined liquid helium

et al. 2017

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“…The idea of using neutrons to measure the condensate fraction of liquid 4 He was originally proposed by Miller et al [1] and Hohenberg and Platzman [2]. Essentially, in high momentum transfer neutron scattering measurements, the energy transfer E is Doppler broadened by the momentum distribution of the atoms in the liquid, n(k).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Bose–Einstein condensation and kinetic energy of liquid⁴He near a free surface

Pearce

Diallo

Glyde

et al. 2004

J. Phys.: Condens. Matter

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We present neutron scattering measurements of Bose-Einstein condensation (BEC) in liquid 4 He adsorbed in thick layers on an MgO substrate to study whether the condensate fraction, n 0 , is increased near a free surface of liquid 4 He. The data show that there is definitely a condensate in the layers adsorbed on the substrate with a condensate fraction comparable to that of bulk liquid 4 He. Two methods of analysis are employed to cross-check the results. The data indicate that the condensate fraction increases significantly when the number of adsorbed layers is reduced. This effect is independent of the analysis technique used. In addition, a significant increase in the kinetic energy of the 4 He atoms is observed when the number of adsorbed layers is reduced.

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“…30 At partial filling of porous media 28,34 and in helium films on surfaces 35,36 , the P-R mode energies differ from the bulk values. At partial filling the P-R mode energy is lower at wave vectors Q ≃ 1Å −1 (the maxon region) and higher in the roton region 18,37 as if the films have a lower density than the bulk density.…”

Section: Figmentioning

confidence: 99%

“…The dynamical structure factor (DSF), S(Q, ω), of liquid 4 He at saturated vapor pressure (SVP) at lower wave vectors, Q ≤ 2.4Å −1 has been investigated in several porous media; aerogel, [12][13][14][15][16][17][18][19] 33 When the porous media is fully filled, the P-R mode energy in all porous media investigated to date is the same as in bulk superfluid 4 He. This is both at low temperature and as a function of temperature within precision 34 .…”

Section: Figmentioning

confidence: 99%

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

et al. 2013

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We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid 4 He confined in 47 Å MCM-41 at T = 0.5 K at wave vectors, Q, beyond the roton wave vector (QR = 1.92 Å−1 ). Measurements beyond the roton require access to high wave vectors (up to Q = 4 Å−1 ) with excellent energy resolution and high statistical precision. The present results show for the first time that at T = 0.5 K the P-R mode in MCM-41 extends out to wave-vector Q ≃ 3.6 Å−1 with the same energy and zero width (within precision) as observed in bulk superfluid 4 He. Layer modes in the roton region are also observed. Specifically, the P-R mode energy, ωQ, increases with Q for Q > QR and reaches a plateau at a maximum energy ωQ = 2∆ where ∆ is the roton energy, ∆ = 0.74 ± 0.01 meV in MCM-41. This upper limit means the P-R mode decays to two rotons when its energy exceeds 2∆. It also means that the P-R mode does not decay to two layers modes. If the P-R could decay to two layer modes, ωQ would plateau at a lower energy, ωQ = 2∆L where ∆L = 0.60 meV is the energy of the roton like minimum of the layer mode. The observation of the P-R mode with energy up to 2∆ shows that the P-R mode and the layer modes are independent modes with apparently little interaction between them.

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Phonons, Rotons, and Layer Modes of LiquidH4ein Aerogel

Cited by 29 publications

References 29 publications

Bulklike excitations in nanoconfined liquid helium

Bulklike excitations in nanoconfined liquid helium

Enhanced Bose–Einstein condensation and kinetic energy of liquid⁴He near a free surface

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

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Phonons, Rotons, and Layer Modes of LiquidH4ein Aerogel

Cited by 29 publications

References 29 publications

Bulklike excitations in nanoconfined liquid helium

Bulklike excitations in nanoconfined liquid helium

Enhanced Bose–Einstein condensation and kinetic energy of liquid4He near a free surface

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

Contact Info

Product

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Enhanced Bose–Einstein condensation and kinetic energy of liquid⁴He near a free surface